1. Field of the Invention
The present invention relates to a vehicular generator-motor system mounted on an internal combustion engine in a vehicle. In particular, the present invention relates to the vehicular generator-motor system that performs for both starting the internal combustion engine and charging a battery mounted in the vehicle.
2. Description of the Related Art
For simplification of equipment or devices mounted in the vehicle, recently, a synchronous rotary machine which operates both as a generator for charging the battery and as a motor for starting the internal combustion engine has been utilized and a various types of systems have been developed heretofore. Among those, there is an approach of using magnetic fields consisting of field windings and permanent magnets to restrain a leakage flux from a claw-shaped magnetic pole, thereby increasing an output power.
The Japanese patent publication No. JP-A-11-136913 discloses a rotor of claw-shaped pole type comprising a rotor coil (field winding) generating magnetic flux, and a pair of pole cores forming so as to surround the rotor coil and having a plurality of claw-shaped pole pieces alternately meshed to each other. The publication also proposes that permanent magnets disposed between the claw-shaped pole pieces alternately meshed are magnetized to the same polarity with that of the magnetic pole to which it attaches, thereby restraining the leakage flux produced between the magnetic pole pieces and thus increasing the output power.
In order to increase the generated output power, there is the other approach in which the permanent magnets are disposed in parallel with the direction of a magnetomotive force produced by the field winding. This approach provides an additional flux to the armature and avoids magnetic saturation in the magnetic path formed in the inner diameter of the field winding. Furthermore, in order to increase the generated output at the time of low speed rotation, there is a technique in which a current flowing through the armature winding is phase-controlled by the inverter to permit a torque current to become negative.
Comparing the synchronous rotary machine used both as the starting motor for the internal combustion engine and as the charging generator for the battery with the synchronous rotary machine used for the generator only, the following problems will arise. Namely, for the purpose of improving a responsibility as the starting motor for the internal combustion engine, it is needed to reduce the number of turn of the field winding, i.e. inductance, to make the time constant small. As the result, when the machine is operated as a generator, it frequently happens that the generated output becomes in shortage and the battery becomes to the overcharging state especially at the time of low speed rotation.
As a measure against above problem, it may be considerable that the current flowing through the armature winding is phase-controlled by the inverter so as to become. This technique, however, is not necessarily excellent in generated efficiencies. Further, when the synchronous rotary machine is operated as a starting motor, a large current is likely to flow through the inverter at the starting stage, thereby the switching elements in the inverter are upsized, and are forced to be equipped with a water cooling system. Likewise, the increase in charging and discharging current results in shortage in the battery life.
In case where the synchronous rotary machine having the field windings and the permanent magnets is used both as a generator and as a motor, the property as to the generator is improved by a function of the additional magnetic flux from the permanent magnets, thereby avoiding the shortage in the generated output.
On the other hand, when the machine is operated as the starting motor for the internal combustion engine, the maximum torque at the starting stage increases, but the induced voltage in the armature increases with increasing rotating speed by the magnetic flux from the permanent magnets. As the result, there is a problem that the motor property at the time of high speed rotation extremely deteriorates because of restraining the armature current.